The present invention generally related to the field of vented battery caps, and more particularly, to the field of multiple plug vented battery caps which are designed to arrest the ignition and/or to minimize the expulsion into the atmosphere. It is well known that a suitable battery vent plug must provide for the expulsion of gases which build up during the chemical charging and discharging action of the battery, while effectively preventing the leakage or evaporation of substantial quantities of the battery electrolyte. To this end, battery vent plugs are normally designed with gaseous connection means for venting the gases produced within the battery to the atmosphere, while providing electrolyte retention means within the battery vent plug for retaining and returning as much of the electrolyte to the battery as is practically feasible. This retention of battery electrolyte is normally accomplished through the use of various baffles and/or gabled floors in the battery vent plug which tend to funnel the battery electrolyte which escapes into the battery vent plug back into the battery cells.
Originally, few provisions were made apart from those described above in order to minimize the chance that a spark in the vicinity of the battery would ignite the battery gases, thereby resulting in the possible explosion of the battery vent plug away from the battery container and/or the explosion of the battery itself. More recently, however, attention has been focused upon the desirability of minimizing the chances that a spark in the vicinity of an operating battery might indeed ignite those gases upon their expulsion to the atmosphere, and attempts have been made to insure that the inadvertent ignition of those gases does not have explosive results. One approach to solving this problem has been to provide a multiple battery vent plug in which gaseous communication is provided from the center of each plug through the body of the plug to four rectangularly widely spced pin hole-like gas outlets in the top cover of the battery for venting these explosive battery gases to the atmosphere, presumably in a diffuse manner. Alternatively, in single battery vent plugs, the interior of the plug which is directly in communication with the battery cell communicates with a gaseous passage disposed under the top surface of the plug by a slot, having a longitudinal member disposed therein, presumably to prevent battery electrolyte from entering the gaseous passage. Two spaced pin hole-like openings are provided on the upper surface of the rather broad cap, again for the purpose of diffusing the explosive battery gases into the atmosphere.
Other designs for venting battery gases safely into the atmosphere have tended to replace these pin hole-like openings with larger cylindrical or rectangular openings into which or next to which are disposed a porous ceramic diffusers. These ceramic diffusers are particularly adapted for use in multiple battery vent plugs which have a hollow body that is adapted for the mounting of such a porous diffuser in a position intermediate between two adjacent battery plugs. One such porous diffuser for a single battery vent plug is disclosed in French Pat. No. 839,808 (1939). Alternatively, another type of microporous membrane is disclosed in U.S. Pat. No. 3,507,708, and U.S. Pat. No. 3,879,227 also discloses such a porous diffuser disposed within a multiple battery vent plug. As with most battery vent plugs, the battery vent plugs described in the above mentioned patents are normally provided with sloping surfaces and/or baffles to prevent or inhibit battery electrolyte from contacting the porous diffuser and/or other vent means.
In particular, in addition to having a porous diffuser located adjacent the atmosphere, U.S. Pat. No. 3,879,227 further discloses a compartment disposed between the porous diffuser and the atmosphere, which compartment has an elongated outlet opening to the atmosphere. The ratio of the volume in cubic inches of the compartment to the area of the elongated outlet in square inches is within a particular range. Presumably, this configuration minimizes the effect of explosions which occur in the area immediately adjacent the porous diffuser, and the size of the compartment and cross sectional area of the elongated opening are selected so as to prevent explosions which occur within the compartment from having serious consequences. To this end, the exterior surface of the compartment is constructed so that upon the ignition of gases within the compartment the elongated opening has a tendency to increase in cross sectional area, thereby venting the ignited gases directly into the atmosphere. Two additional types of multiple battery vent plugs are disclosed in U.S. Pat. Nos. 3,992,226 and 4,086,395 (which is a parent of the present application). Both of these patents provide structures with at least one venting orifice therein directed away from the battery when fitted into the battery vents, and both plugs of these patents have internal configurations which help to eliminate any possibility of the battery electrolyte passing from the battery through the vent plug.
Furthermore, at least one type of vent plug is known wherein a separate top member of the plug fastens to the inside of a bottom member that fits into the battery vent openings. In that instance, prong members project upwardly form the inside of the base member and engage a rim which runs along the inside of the top member to securely fasten the two members together.
Other patents which generally show multiple battery vent plugs include U.S. Pat. Nos. 3,284,244, 3,265,538, 3,369,940 and 3,597,280. Other battery vent patents include U.S. Pat. Nos. 3,466,199, 2,670,396 and the references cited thereon.